Femtosecond-laser-irradiation-induced structural organization and crystallinity of Bi2WO6

Abstract

controlling the structural organization and crystallinity of functional oxides is key to enhancing their performance in technological applications. in this work, we report a strong enhancement of the structural organization and crystallinity of Bi 2 Wo 6 samples synthetized by a microwave-assisted hydrothermal method after exposing them to femtosecond laser irradiation. X-ray diffraction, UVvis and Raman spectroscopies, photoluminescence emissions, energy dispersive spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy were employed to characterize the as-synthetized samples. To complement and rationalize the experimental results, firstprinciples calculations were employed to study the effects of femtosecond laser irradiation. Structural and electronic effects induced by femtosecond laser irradiation enhance the long-range crystallinity while decreasing the free carrier density, as it takes place in the amorphous and liquid states. these effects can be considered a clear cut case of surface-enhanced Raman scattering.Bismuth tungstate, Bi 2 WO 6 (BWO), is an important n-type semiconductor with a narrowband gap energy (E gap ) of 2.8 eV that allows efficient absorption of visible light (λ > 400 nm) and has been widely studied due to its wide range of properties, such as ferroelectricity, piezoelectricity, pyroelectricity, nonlinear dielectric susceptibility, and photoluminescent emissions 1,2 . The multifunctionality of this material has been demonstrated on its photocatalytic activity 3-22 , photocatalytic degradation of drugs 23 , dyes 24-26 alcohols 27 , and phenol 28 , environmental purification, energy conversion 29 , and production of sustainable and combustible compounds 3 . Recently, some works attested this material to be efficient in water splitting for hydrogen generation 30-32 , for shielding against low-energy gamma rays 33 and for CT/IR imaging and photothermal/photodynamic therapy of tumours 34,35 .BWO has an orthorhombic structure and belongs to the Aurivillius family. It is formed by alternating (Bi 2 O 2 ) n 2n+ and perovskite (WO 4 ) n 2n layers 36 , which are composed of (WO 6 ) octahedral layers and (Bi-O-Bi) layers. Their crystal structure can also be described by alternating [Bi 2 O 2 ] 2+ slabs and [WO 4 ] 2− slabs, with oxygen atoms shared between the slabs to create chemical bonds. An important characteristic of this structure is that local environments of both W and Bi cations are highly distorted 37 . The off-centre octahedral distortions are a general feature of the structural chemistry of d 0 metal cations. Each W cation is coordinated with six O atoms to form [WO 6 ] octahedral clusters that are connected to each other by corner-sharing O atoms. The (Bi 2 O 2 ) 2+ layers are sandwiched between (WO 6 ) octahedral layers. From an electronic point of view, BWO presents hybridized valence bands occupied by the Bi 6 s and O 2p states that shift the absorption band edge towards the visible region, with the concomitant appearance of a narrow absorpt...

Unconventional Disorder by Femtosecond Laser Irradiation in Fe2O3

“…In this way, different semiconductors can be obtained depending on the desired property, characterizing a more conductive behavior of the irradiated samples in the medium-range order. 67 These findings also point to the existence of electronic levels located within the prohibited band, which are associated with the presence of defects, such as distortions and vacancies, responsible for causing a structural lattice disorder, previously observed in XRD and Raman analyses.…”

Synthesis and evaluation of photocatalytic and photoluminescent properties of Zn2+-doped Bi2WO6

“…The absorption is a result of the hybridization of O 2p and Bi 6s orbitals forming the valence band (VB), while the conduction band (CB) has major contributions from the W 5d orbitals. 26,29…”

“…As shown in the literature, Bi 2 WO 6 is a direct optical transition semiconductor. 29 Fig. 6 represents the gap energies that are estimated at: 2.93, 2.87, 2.95, 2.82 and 2.94 eV for the respective samples: Bi 2 WO 6 , Bi 2 WO 6 :1% Zn 2+ , Bi 2 WO 6 :2% Zn 2+ , Bi 2 WO 6 :4% Zn 2+ and Bi 2 WO 6 :8% Zn 2+ .…”

“…The absorption is a result of the hybridization of O 2p and Bi 6s orbitals forming the valence band (VB), while the conduction band (CB) has major contributions from the W 5d orbitals. 26,29 The gap energy of Bi 2 WO 6 and Bi 2 WO 6 :x% Zn 2+ was estimated from the Kubelka-Munk transformation. As shown in the literature, Bi 2 WO 6 is a direct optical transition semiconductor.…”

Laser Synthesis and Microfabrication of Micro/Nanostructured Materials Toward Energy Conversion and Storage

“…By tuning the laser processing parameters, including the scanning speed, laser wavelength and output power, the optimum perovskite films with high crystallinity and perovskite solar cells with high energy conversion efficiency and durability were successfully fabricated. Besides the crystallization of perovskite films for PSCs, the fs laser processing Bi 2 WO 6 with a strong enhancement of the structural organization and crystallinity were also reported [ 99 ].…”